Stop consonants are made when the oral tract is closed at some point and the release of air is completely obstructed. Fricative consonants are made with some constriction in the oral tract so that the release of air causes some degree of friction. A speaker of English may turn stops into fricatives, maintaining the place of articulation. So bilabial stops are produced as bilabial fricatives, velar stops are produced as velar fricatives, and so on. This is what the Igbo 1 speaker does to some selected stops.